Yeah, its called chaining, basically after you get an assault streak any kills you obtain with it count towards your next streak in your strike chain. However if you've already obtained the highest streak in your three rewards or if you die it doesn't count anymore. On a side note, how do you get triple kills with the trinity rocket? I'd like some advice because half the time the first two lock on rockets don't lock on and fly to the side and for the third rocket I'll have it on target and not move anything but it'll start sliding to one side and miss.

So what about the Sentry Gun, then?Does that add kills to my streak as long as it kills some people while I'm still on that same life? Or does it have to kill a certain number of people before it adds a point to my streak counter?

As for getting triple kills with the TR, it's AAAALLLLL luck. You need a tightly packed group, then just send all three rockets blazing into the pack. No amount of Blast Shield and Riot Shield equipment will let them survive such a thing.